You could probably use Google Maps as a way to make a kind of zombie survival game. When a player creates a new character, it uses wherever they are as the starting point, then must navigate the terrain. Zombie population could be based upon CIA world book populations of real cities, and infrastructure could be mapped out.
I started making a Game Maker game that was similar to this. The scope was smaller, where you were a guy who just fled a zombie infected city and found a small, slightly ruined house in the woods. From there you had to kind of carve out a living. It was have day and night cycles, where day was meant for scavenging, finding other survivors, and building up your camp. Night would end up in siege mode, where zombies would be attracted to your base and you'd have to defend while they tried to break in. After each night, the map would expand slightly giving you more territory to explore (reflecting your confidence in the terrain).
As the game went on, you'd be able to find other survivors and put them to work doing various tasks. Some could be medics, builders, soldiers, farmers, etc. They'd be able to help out around the camp with various tasks. At first new survivors would be bite-free, but as the game went on each new survivor would have increasing odds of having a hidden bite, meaning that they might turn while inside your camp. As a result, the further along in the game you might have to decide how much you might want that medic, or that soldier, or that farmer.
I think I have the demo I started making somewhere. Wasn't much. Zombies kind of stumbled around a forest while the player could shoot or use an ax. Needed more work.
EDIT: Why the hell not.
These Woods, the not-even-a-demo or proof-of-concept. Arrow keys move you, when you find the gun, CTRL shoots, and if you find the axe it just gives you a chance to kill a zombie if they hit you.
Also F4 will make it Fullscreen. Man, I don't know what I was thinking of for how shit worked. If it seems like a zombie isn't dying, that's because I went with "Only head shots kill a zombie!", which means when you shoot one it rolls a dice and on 9 or 10 or something it gets a head shot.